This project is designed to examine the neuroendocrine and gonadal regulation of FSH in the female, specifically defining the relative contributions of inhibins A and B to the control of FSH secretion and folliculogenesis during the normal menstrual cycle. In this past year, the investigators have completed a large study in which they determined that reproductive aging is marked by decreased secretion of dimeric inhibin and that these changes occur well before there is any evidence of cycle irregularity or before there are increases in FSH. The investigators showed that in the early follicular phase inhibin B was lower and FSH higher in women 35-46 (n=21) compared with <35 (n=23), that in the mid and late follicular phase, inhibin B was lower and estradiol higher in the older cycling women with no difference in FSH. The investigators have also studied 3 individuals 10 years apart and determined that in longitudinal studies there is also a very clear decrease in inhibin A levels during the luteal phase with reproductive aging. These studies provide definitive evidence for an endocrine role of inhibin B in the control of FSH secretion in women.